(1) Field of the Invention
The present invention relates to a light-emitting device and an image forming device, and in particular to a technology for correcting a change in a light emission amount occurring when surrounding temperature changes, with high accuracy.
(2) Description of the Related Art
Conventional technology discloses a technology of applying organic light-emitting diodes (OLEDs) to optical writing devices executing optical writing onto a photoreceptor, for the purpose of downsizing and reducing the cost of image forming devices.
An OLED has a light-emitting characteristic such that, even when a driving current amount input to the OLED does not change, the amount of light emitted by the OLED changes when the temperature of the OLED changes. The temperature of an OLED is under the influence of a surrounding temperature of the OLED. For instance, as illustrated in FIG. 15, the light amount ratio of an OLED decreases as the surrounding temperature of the OLED increases from temperature T1 to temperature T2, which is higher than temperature T1. Such a decrease in the light amount emitted by an OLED may influence an electrostatic latent image that is formed on a photoreceptor, and therefore may unfortunately bring about a decrease in image quality.
Application of OLEDs has been considered in technical fields other than image forming devices as well. Therefore, stabilization of light amounts emitted by OLEDs is an essential problem to be solved in various technical fields. In relation with this problem, for instance, Japanese Patent No. 5343073 discloses a technology for correcting a driving current amount of an OLED. In specific, this conventional technology discloses providing beforehand a table associating different surrounding temperatures each with correction data to be applied to a driving current amount to yield a desired light amount, and correcting a drive current amount of an OLED by referring to this table based on a surrounding temperature of the OLED that is measured by using a temperature sensor. This achieves causing an OLED to emit a desired light amount even when surrounding temperature changes.
Meanwhile, how the light amount of an OLED changes relative to surrounding temperature (hereinafter called a temperature characteristic of an OLED) is affected by a driving current amount supplied to the OLED. That is, a change in the driving current amount input to an OLED affects the temperature characteristic of the OLED. As illustrated in FIG. 16, the gap between the light amount ratio at surrounding temperature T1 (i.e. 100%) and the light amount ratio at surrounding temperature and the light amount at surrounding temperature T2 is greater when the OLED is supplied with a relatively great driving current amount (I1) than when the OLED is supplied with a relatively small driving current amount (I3).
In the technical field of image forming devices, optical writing is executed by collecting light emitted from linearly arranged OLEDs onto a photoreceptor via a rod lens array. However, because the OLEDs are disposed at different positions with respect to the rod lens array, image forming efficiency may vary between the OLEDS. Therefore, even when all the OLEDs are provided with the same driving current amount to cause the OLEDs to emit the same light amount, different areas of the photoreceptor, each corresponding to one pixel, are exposed to different light amounts (i.e., different light exposure amounts).
Light exposure amounts of different areas of the photoreceptor can be made uniform by adjusting driving currents that are input to different OLEDs. However, when OLEDs are supplied with different driving current amounts, light amounts emitted by different OLEDs change in a different manner in response to a change in surrounding temperature. Due to this, the technology disclosed in Japanese Patent No. 5343073 of applying the same correction data to all OLEDs cannot appropriately correct the change in light amounts emitted by the OLEDs occurring when surrounding temperature changes.